Production of ethylene



United States Patent 3,278,630 PRODUCTION OF ETHYLENE Robert L.Hartnett, Texas City, Tex., assignor to Monsanto Company, St. Louis,Mo., a corporation of Delaware No Drawing. Filed Apr. 21, 1964, Ser. No.361,590 4 Claims. (Cl. 260-6833) This invention relates to an improvedprocess for the production of olefins from saturated hydrocarbons. Moreparticularly, it relates to the production of ethylene from ethane.

It is well known that olefins can be obtained by thermal decompositionof petroleum derived hydrocarbons. Ethylene can be obtained, forexample, by thermal conversion of light saturated hydrocarbons such asethane and/ or propane. However, in such a process the gaseousconversion product contains, in addition to the desired ethylene,significant amounts of other products such as methane, propylene,acetylene, butenes, and the like. In order to recover the ethylene insufficiently pure form for its utilization, the gaseous thermalconversion product must be processed by fractionation in a series ofsteps requiring fairly elaborate equipment and time consumingoperations. Furthermore, non-gaseous hydrocarbons such as oils and tarsand normally cyclic hydrocarbons are formed simultaneously with theethylene. Provision must be made for removal of such contaminantsbecause they lead to fouling of the apparatus and equipment. Thus,despite extensive studies which have been made on cracking of lighthydrocarbons to produce ethylene, there are still some disadvantages incommercial production by this method.

Some of the problems inherent in the production of ethylene by crackingtechniques can be obviated by producing this hydrocarbon in a relativelypure state by catalytic dehydrogenation of ethane. However, the art hasthus far failed to provide a continuous process for the dehydrogenationof ethane to ethylene which is not subject to a number of drawbacks.Known catalysts for the dehydrogenation suffer from deficiencies in thatthey either result in low conversion to dehydrogenation products or tolow yields of ethylene or are deficient in both respects. Prior artcatalysts, too, become readily fouled with carbon deposits which renderthem ineffective in the dehydrogenation process and necessitate frequentand sometimes expensive regeneration. The advantages of a processwherein conversion of ethane to ethylene can be effected with feweroperational steps and less by-product formation are, therefore,immediately obvious.

A relatively simple process for producing ethylene from ethane in goodconversion and high yields and with comparatively little loss tonon-useful by-products has been described and claimed in a co-pendingapplication, Serial No. 361,589, filed April 21, 1964. In this process,ethane is reacted with hydrogen chloride and oxygen at an elevatedtemperature in the presence of activated alumina. It has now beendiscovered that either the conversion or yields or both in such aprocess can be significantly improved if instead of activated aluminaalone, a catalyst consisting of calcium chloride supported on activatedalumina is employed for the reaction.

According to the present invention, then, ethylene is produced bybringing a mixture of ethane, hydrogen chloride and oxygen in contact atelevated temperatures with a catalyst consisting essentially of a minoramount of calcium chloride supported on activated alumina. Only smallamounts of chlorinated lay-products are produced which are readilyseparable from ethylene, fewer steps are required for recovery ofethylene than are generally employed in the prior art, and the hydrogenchloride emoloyed can be continuously recycled in the process.

3,278,630 Patented Oct. 11, 1966 ICE EXAMPLE 1 A tubular reactor about 6ft. long and 60 mm. in diameter wrapped with Nichrome wire for heatingand covered with asbestos insulation was employed as the reactor. Athermowell containing thermocouples for measuring temperatures wascentrally positioned in the reactor extending throughout its length.Approximately 1000 g. of a catalyst consisting of 5% by weight ofcalcium chloride supported on activated alumina was charged to thereactor and fluidized by passing nitrogen up through it while thereactor was brought up to reaction temperature. The catalyst had beenprepared by dissolving calcium chloride in methanol, saturating theactivated alumina with the solution, and drying the resulting slurry ina rotary vacuum drier.

Hydrogen chloride and oxygen at approximate rates of 0.06 and 0.03s.c.f.m. (standard cubic feet per minute), respectively, were passedthrough rotameters into a common manifold where they were mixed and fromwhich they were then introduced into the bottom inlet of the reactor tocontact the fluidized catalyst maintained at a temperature from about400 C. to about 600 C. Ethane, at a rate of about 0.06 s.c.f.m., was fedseparately through a rotameter and injected simultaneously into thefluidized catalyst in the reactor at a point about 5 inches above thebottom inlet. As the reactants were introduced, the

- flow of nitrogen was appropriately reduced so that the velocity of theentering gaseous reactants helped to maintain the catalyst in thefluidized state. Contact time was approximately 4.7 seconds.

Eflluent gases from the top of the reactor were passed directly into agas chromatograph for analysis. From the analysis of the reactionproduct collected at various temperature levels, total conversion ofethane, conversion of ethane to ethylene, and yields of ethylene werecalculated. Results are presented in Table 1 below.

' Table 1 Total Conv. to Yield of Temperature, C. C2115 C2114, CzHr,

O0nv., percent percent percent EXAMPLE 2 The experiment of Example 1 wasrepeated except that activated alumina was substituted for the catalystemployed in that example. The average conversion of ethane, conversionto ethylene, and yield of ethylene obtained using activated aluminawithin the optimum temperature range of 550 to 590 C. are presented inTable 2 below. Alongside these values are tabulated the average valuesobtained under comparable optimum temperature conditions with thecatalyst consisting of calcium chloride supported on activated aluminaused in Example 1. These data provide convincing evidence thatimpregnation of activated alumina with a minor amount of calciumchloride results in a highly improved catalyst for the production ofethylene from ethane via reaction of the latter with hydrogen chlorideand oxygen. Moreover, this catalyst can be used at lower temperaturesthan can activated alumina alone.

It is readily apparent that various modifications of reaction conditionsgiven in the examples can be made without departing from the scope ofthe invention. In the preferred embodiment of the invention, thecatalyst is employed in the fluidized or pseudo liquid state. It ismaintained in a fluid or suspended state by the gaseous reactantsthemselves or, optionally, by the use of an additional inert gasintroduced from an outside source. The use of a fixed bed operation,however, is not precluded.

The catalyst of the process is readily prepared by saturating activatedalumina with a solution, aqueous or otherwise, of calcium chloride andfiltering and drying the impregnated alumina. Further drying may beelfected by means of a flow of nitrogen (or other inert gas), hydrogenchloride and/or air through the mass of catalyst while it is beingheated to reaction temperature after it has been charged to the reactor.A more active catalyst is prepared from a methanolic solution of calciumchloride. Better catalytic activity can probably be attained with acatalyst prepared and dried under vacuum. Generally, amounts of calciumchloride from about 1% to about 15% by weight of the total catalystcomposition are supported on the activated alumina. The preferredcatalyst compositions contain from about 5% to about calcium chloride.

The preferred method of introducing the reactants is that which isexemplified, that is, the hydrogen chloride and oxygen are introducedinto the bottom of the reactor while ethane is injected at a pointsomewhat above the bottom inlet point. The point of ethane injection issuitably located at a distance of from about 5% to about 20% of thereactor length above the inlet of the other reactants. Optimum resultsare obtained with the ethane being injected at a point from about 7 toabout 10% of the reactor length above the bottom inlet. The reaction maybe carried out by mixing the ethane, hydrogen chloride and oxygen or airand passing the mixture into the reactor, or by introducing oxygen orair into a mixture of ethane and hydrogen chloride. These latter methodsare, however, much less satisfactory than the preferred one. Precautionshould be taken to avoid mixing ethane and oxygen in the absence ofhydrogen chloride to prevent creation of possible hazardous conditions.

As is evident from the examples, the relative proportions of thereactants may vary considerably. Ratios of ethane to hydrogen chlorideto oxygen varying from 1:0.5:0.2 to 1:2:1 can be used. If is understoodthat the oxygen for the reaction may, of course, be supplied in the formof air and when air is used the mole ratio of ethane to hydrogenchloride to air may vary from 110.521 to 1:225. Preferably, the moleratio when oxygen is employed is maintained at about l:l:0.3 andcorrespondingly at l:l:1.5 when air is used. Since little hydrogenchloride is consumed in the reaction, only very small amounts, if any,of hydrogen chloride need be fed once the reaction has been initiated ifprovision is made for recycle of the hydrogen chloride.

Contact time is not a critical variable and may vary from about 1 toabout 30 seconds. Preferred contact times are those from about 5 toabout 20 seconds.

Reaction temperature is a critical factor. The temperature must bemaintained above about 390 C. to effect the reaction. Generally, asuitable temperature range for the reaction is that from 400 to 600 C.,although temperatures up to about 625 C. or 650 C. can be employed. Attoo high temperatures, however, carbon begins to deposit on thecatalyst. Preferably, the temperature of the reaction is maintained fromabout 550 to about 590 C.

What is claimed is:

1. A process for the production of ethylene which comprises contacting amixture of ethane, hydrogen chloride and oxygen in a mole ratio in therange from about 1:05:02 to 1:2:1 with a catalyst consisting essentiallyof calcium chloride supported on activated alumina at a temperaturewithin the range from about 400 to about 600 C.

2. A process for the production of ethylene which comprises contacting amixture of ethane, hydrogen chloride and oxygen in a mole ratio in therange from about 1:05:02 to 1:2:1 with a catalyst consisting essentiallyof from about 1% to about 15% by weight based on the total catalystcomposition of calcium chloride supported on activated alumina at atemperature within the range from about 400 to about 600 C.

3. A process for the production of ethylene which comprises contacting amixture of ethane, hydrogen chloride and oxygen in a mole ratio of 1:1:0.3 at a temperature within the range from about 550 to about 590 C.with a catalyst consisting essentially of from about 5% to about 10% byweight of calcium chloride supported on activated alumina.

4. A process for the production of ethylene which comprises passingethane, hydrogen chloride and oxygen in a mole ratio of 1:1:0.3 througha fluidized bed of catalyst consisting essentially of from about 1% toabout 15% by weight of calcium chloride supported on activated aluminamaintained at a temperature from about 400 to about 600 C. byintroducing hydrogen chloride admixed with oxygen into the bottom ofsaid bed while injecting ethane at a point which is from about 5% toabout 20% of the reactor length above the bottom of said bed.

References Cited by the Examiner UNITED STATES PATENTS 2,397,638 4/1946Bell et al. 260683 2,921,101 1/1960 Magovern 260-680 3,207,806 9/1965Bajars 260-680 DELBERT E. GANTZ, Primary Examiner.

G. E. SCHMITKONS, Assistant Examiner.

1. A PROCESS FOR THE PRODUCTION OF ETHYLENE WHICH COMPRISES CONTACTING AMIXTURE OF ETHANE, HYDROGEN CHLORIDE AND OXYGEN IN A MOLE RATIO IN THERANGE FROM ABOUT 1:0.5:02 TO 1:2:1 WITH A CATALYST CONSISTINGESSENTIALLY OF CALCIUM CHLORIDE SUPPORTED ON ACTIVATED ALUMINA AT ATEMPERATURE WITHIN THE RANGE FROM ABOUT 400* TO ABOUT 600*C.